Black light-blocking material

Abstract

Provided is a light shielding member having low gloss and high blackness, as well as excellent workability.　A light shielding layer 3 containing black fine particles 32, low-refractive-index nanoparticles 33, and a resin component 31 is formed on at least one surface of a substrate. The average particle diameter of the black fine particles 32 is 0.1-50 µm, and the average particle diameter of the low-refractive-index nanoparticles 33 is 1-300 nm. Porous carbon is preferred for use as the black fine particles 32, and magnesium fluoride particles and silicon oxide particles are preferred for use as the low-refractive-index nanoparticles 33.

Description

[Technical Field]

[0001] The present invention relates to a black light-shielding member, and more particularly to a black light-shielding member that can be suitably used in optical devices such as camera units of mobile phones including smartphones. [Background technology]

[0002] Light-blocking members are generally used in the lens aperture, shutter, and lens spacer of a camera. Known examples of such light-shielding materials include black films in which a predetermined uneven shape is formed on the surface of a black polyester substrate containing a black pigment such as carbon black. In the above configuration, by controlling the fine uneven shape on the surface of the light-shielding layer, light is effectively scattered, and the black pigment absorbs the light, reducing reflected light and achieving low gloss. Methods for forming the uneven shape include a method of coating the substrate surface with a light-shielding layer containing a matting agent and a method of roughening the substrate surface by a technique such as sandblasting.

[0003] Patent Document 1 describes that the above method is used to adjust the arithmetic mean roughness Ra of the surface of a light-shielding member according to JIS B0601:2001 to 0.5 μm or more, and the difference between the maximum peak height Rp and the maximum valley depth Rv (Rp-Rv) to less than 3. It is also shown that a light-shielding member having such a surface shape has excellent anti-reflection performance even when made thin, has high hardness, and has excellent adhesion between the light-shielding layer and the film substrate, and therefore can maintain excellent low glossiness for a long period of time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. WO2018 / 052044 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, there has been a demand for light-shielding materials for optical devices that have a high level of blackness and that emphasize blackness in order to improve design. However, conventional light-shielding materials have a tendency to scatter light on the surface of the light-shielding layer, resulting in a whitish appearance and a lack of prominent blackness, making it difficult to achieve both low gloss and high blackness. While increasing the amount of black microparticles can improve the blackness while maintaining low gloss, this can lead to problems such as the light-shielding coating film becoming more susceptible to shedding and reduced processability. The present invention has been made in view of the above circumstances, and has as its object to provide a light-shielding member that has low gloss, high blackness, and excellent processability. [Means for solving the problem]

[0006] In view of the above problems, the present inventors conducted extensive research and discovered that the above problems can be solved by adding low-refractive-index nanoparticles together with black microparticles to the resin component of a black light-shielding member having a substrate and a light-shielding layer formed on at least one surface of the substrate, and thus arrived at the present invention. That is, the black light-shielding member of the present invention is a black light-shielding member comprising a substrate and a light-shielding layer formed on at least one surface of the substrate, and characterized in that the light-shielding layer contains black microparticles, low-refractive-index nanoparticles, and a resin component.

[0007] The black fine particles preferably contain porous carbon. The low refractive index nanoparticles preferably include at least one selected from magnesium fluoride particles, calcium fluoride particles, lithium fluoride particles, calcium carbonate particles, and silicon oxide (silica) particles. Furthermore, the low refractive index nanoparticles preferably contain magnesium fluoride particles and silicon oxide particles. The low refractive index nanoparticles may include hollow nanoparticles. The hollow nanoparticles may include hollow silica particles. The total content of the black fine particles and low refractive index nanoparticles in the light-shielding layer is preferably 50% to 95% of the volume of the entire light-shielding layer. Furthermore, it is preferable that the average particle size of the black microparticles is 0.1 μm to 50 μm, the average particle size of the low refractive index nanoparticles is 1 nm to 200 nm, and the low refractive index nanoparticles account for 1 volume % to 50 volume % of the total amount of the black microparticles and the low refractive index nanoparticles. Furthermore, it is preferable that the glossiness of the surface of the black light-shielding member on which the light-shielding layer is formed is 1% or less for incident light at an incident angle of 60°, and the L value is 10 or less. The average thickness of the light-shielding layer is preferably 1 μm to 100 μm. [Effects of the Invention]

[0008] The black light-shielding member of the present invention has low gloss, high blackness, and excellent design properties, and therefore can be suitably used as a camera unit for mobile phones such as smartphones. Furthermore, the black light-shielding member of the present invention has good adhesion of the light-shielding layer, so peeling of the light-shielding layer coating is suppressed even during punching, and the black light-shielding member has excellent processability. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view schematically illustrating a configuration of a light-shielding member according to an embodiment of the present invention. [Figure 2] 1A is a schematic diagram showing the attenuation behavior of incident light in a light-shielding member of the present invention, and FIG. 1B is a schematic diagram showing the attenuation behavior of incident light in a light-shielding member that does not contain low-refractive-index nanoparticles in the light-shielding layer. [Figure 3] 1A is a cross-sectional view showing the configuration of a light-shielding member of Reference Example 1 and FIG. 1B is a cross-sectional view showing the configuration of a light-shielding member of Reference Example 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail. In this specification, the symbol "to" indicating a range of values ​​indicates a range that includes the values ​​stated as the upper and lower limits. When a unit is stated only for the upper limit of a range of values, this means that the lower limit is expressed in the same unit as the upper limit. In the numerical ranges described in stages in this specification, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples. In this specification, the content or amount of each component in a composition means, when multiple substances corresponding to each component are present in the composition, the total content or amount of the multiple substances present in the composition, unless otherwise specified.

[0011] 1 is a cross-sectional view showing a configuration of a black light-shielding member 1 according to an embodiment of the present invention. The black light-shielding member 1 of the present invention includes a substrate 2 and a light-shielding layer 3 formed on at least one surface of the substrate 2, and the light-shielding layer 3 contains black fine particles 32, low-refractive-index nanoparticles 33, and a resin component 31. In the present invention, the low refractive index nanoparticles 33 are dispersed in the resin component 31, so that the refractive index of the light-shielding layer 3 is reduced, and the light-shielding layer 3 and the air layer (n d = 1.00), the difference in refractive index between the black fine particles and the black shading layer 3 decreases, reducing the amount of diffusely reflected light on the surface of the black shading layer 3. Furthermore, the diffusely reflected light is reflected and absorbed by the black fine particles, resulting in significant attenuation of the light. For this reason, it is believed that the black shading member 1 of the present invention can achieve low gloss and high blackness. Specific material configurations of the black light-shielding member of the present invention will be described below.

[0012] (1) Base material The substrate used in the present invention is not particularly limited and may be transparent or opaque. Materials that can be used for the substrate in the present invention include resins, metals, and glass. Examples of materials for the resin substrate include polyolefins such as polyethylene, polypropylene, ethylene-propylene copolymers, and copolymers of ethylene and α-olefins having 4 or more carbon atoms; polyesters such as polyethylene terephthalate; polyamides such as nylon; other general-purpose plastics such as ethylene-vinyl acetate copolymers, polyvinyl chloride, and polyvinyl acetate; and engineering plastics such as polycarbonate and polyimide.

[0013] Examples of metal substrates include metal substrates made of metals such as gold, silver, copper, aluminum, titanium, zinc, beryllium, nickel, and tin, and alloy substrates made of alloys such as phosphor bronze, copper-nickel, copper-beryllium, stainless steel, brass, and duralumin. The glass substrate is not particularly limited, but for example, ultra-thin glass (G-Leaf (registered trademark), manufactured by Nippon Electric Glass Co., Ltd.) can be used.

[0014] Among these materials, biaxially oriented polyethylene terephthalate substrates are preferred because they have relatively high strength, are economical, and are highly versatile. Furthermore, from the viewpoint of heat resistance, polyimide substrates are preferred, and when even higher heat resistance is required, it is preferable to use a metal substrate made of copper. In the case of resin substrates, better light-blocking properties can be obtained by kneading in advance a black colorant such as carbon black or aniline black to adjust the optical density to 2 or more, preferably 4 or more.

[0015] The thickness of the substrate is not particularly limited, but when a resin substrate is used, it is preferably 2 μm to 250 μm, and more preferably 4 μm to 100 μm. By setting the thickness of the substrate within the above range, it can be suitably used for small and thin optical components. Furthermore, when used in optical devices such as camera units for mobile phones, the thickness is preferably 4 μm to 20 μm. When a metal substrate is used, the thickness of the substrate is preferably 6 μm to 40 μm, and when used in optical devices such as camera units of mobile phones, the thickness is preferably 10 μm to 20 μm. When a glass substrate is used, the thickness of the substrate is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and when used in optical devices such as camera units of mobile phones, the thickness is preferably 10 μm to 35 μm.

[0016] The substrate may be flat, or may have a matte surface to form irregularities (roughened portions). The matte finish can control the irregular shape of the surface of the light-shielding member after coating with a light-shielding layer, and can also improve adhesion between the substrate and the light-shielding layer. The matte finish method is not particularly limited, and known methods can be used. For example, when the substrate is a resin substrate, chemical etching, blasting, embossing, calendaring, corona discharge, plasma discharge, chemical matting using a resin and a surface-roughening agent, and the like can be used. Alternatively, a matting agent can be directly incorporated into the substrate to form irregularities on the surface of the resin substrate. Among the above-mentioned processing methods, blasting, particularly sandblasting, is preferred from the viewpoints of ease of shape control, economy, and ease of handling. In the sandblasting method, the surface properties can be controlled by adjusting the particle size of the abrasive used, the spray pressure, etc. In the embossing method, the surface properties can be controlled by adjusting the shape and pressure of the embossing roll. On the other hand, when the substrate is a metal substrate film, the surface can be made uneven by blackening treatment, blasting treatment, etching treatment or the like.

[0017] (2) Anchor layer Before providing a light-shielding layer on at least one surface of the substrate, an anchor layer can be provided to improve adhesion between the substrate and the light-shielding layer. Examples of anchor layers that can be used include urea-based resin layers, melamine-based resin layers, urethane-based resin layers, and polyester-based resin layers. For example, a urethane-based resin layer can be obtained by applying a solution containing a polyisocyanate and an active hydrogen-containing compound such as a diamine or diol to the substrate surface and curing it. Furthermore, a urea-based resin or melamine-based resin can be obtained by applying a solution containing a water-soluble urea-based resin or water-soluble melamine-based resin to the substrate surface and curing it. A polyester-based resin can be obtained by applying a solution dissolved or diluted in an organic solvent (methyl ethyl ketone, toluene, etc.) to the substrate surface and drying it.

[0018] (3) Light shielding layer The light-shielding layer of the present invention contains a resin component, black fine particles, and low-refractive-index nanoparticles. Each component will be explained below.

[0019] 1) Resin component The resin component serves as a binder for the black microparticles and low-refractive-index nanoparticles. There are no particular limitations on the material of the resin component, and either a thermoplastic resin or a thermosetting resin can be used. Specific examples of thermosetting resins include acrylic resins, urethane resins, phenolic resins, melamine resins, urea resins, diallyl phthalate resins, unsaturated polyester resins, epoxy resins, and alkyd resins. Examples of thermoplastic resins include polyacrylic ester resins, polyvinyl chloride resins, butyral resins, and styrene-butadiene copolymer resins. From the viewpoints of heat resistance, moisture resistance, solvent resistance, and surface hardness, it is preferable to use a thermosetting resin. In consideration of flexibility and toughness of the coating, among thermosetting resins, acrylic resin is particularly preferable. On the other hand, when toughness of the coating is not particularly required, it is preferable to use a thermoplastic acrylic resin because the heat curing step can be omitted.

[0020] Adding a curing agent as a constituent of the light-shielding layer can promote crosslinking of the resin component. Examples of curing agents that can be used include urea compounds, melamine compounds, isocyanate compounds, epoxy compounds, aziridine compounds, and oxazoline compounds, each having a functional group. Among these, isocyanate compounds are particularly preferred. The blending ratio of the curing agent is preferably 10% by mass to 50% by mass relative to 100% by mass of the resin component. Adding a curing agent in the above range can provide a light-shielding layer with more suitable hardness, and the surface shape of the light-shielding layer can be maintained for a long period of time, even when the light-shielding layer slides against other components, resulting in sustained low gloss. When a curing agent is used, a reaction catalyst can be used in combination to accelerate the reaction. Examples of the reaction catalyst include ammonia and ammonium chloride. The mixing ratio of the reaction catalyst is preferably in the range of 0.1% by mass to 10% by mass relative to 100% by mass of the curing agent.

[0021] 2) Black fine particles The black light-shielding member of the present invention is characterized in that the light-shielding layer contains black fine particles. As shown in Figure 1, the black fine particles 32 form a fine uneven shape on the surface of the light-shielding layer 3. This uneven surface scatters light, thereby reducing gloss. Furthermore, the black fine particles 32 absorb light, and the repeated scattering and absorption reduces reflected light, achieving even lower gloss. FIG. 1 shows a configuration in which a light-shielding layer 3 containing black fine particles 32 is coated on the surface of a flat substrate 2, but as described above, a substrate having an uneven surface formed by matte processing can also be used. In the present invention, in order to achieve a desired gloss level, the uneven shape of the surface of the light-shielding layer 3 can be controlled according to existing methods. The surface shape of the light-shielding layer 3 can be controlled by adjusting the surface shape of the substrate 2, the particle size, particle size distribution, and content of the black fine particles 32, and the film thickness of the light-shielding layer 3. It can also be controlled by adjusting the type of solvent and solids concentration when preparing the coating liquid, and the amount applied to the substrate. Furthermore, it can also be controlled by adjusting the coating film production conditions, such as the application method of the coating liquid, the drying temperature, time, and air volume during drying.

[0022] The average particle size of the black fine particles of the present invention is not particularly limited as long as a light-shielding layer having a desired surface shape can be obtained, but is preferably 0.1 μm to 50 μm, and more preferably 1 μm to 10 μm. By setting the average particle size of the black fine particles within the above range, fine irregularities are formed on the surface of the light-shielding layer, thereby further reducing the glossiness. The content of the black microparticles varies depending on the average particle size and particle size distribution of the black microparticles, the film thickness of the light-shielding layer, and the surface shape of the substrate, but is preferably 25% to 93% by volume, and more preferably 50% to 90% by volume, of the entire light-shielding layer being 100% by volume. By setting the content of the black fine particles within the above range, it is possible to achieve both better black color and low gloss. The volume content (volume occupancy) of the black fine particles in the light-shielding layer can be calculated from a cross-sectional photograph of the light-shielding layer by image analysis or the like, and converted into an area occupancy.

[0023] The black microparticles may be either resin particles or inorganic particles. Examples of materials for resin particles include melamine resin, benzoguanamine resin, benzoguanamine / melamine / formalin condensate, acrylic resin, urethane resin, styrene resin, fluororesin, and silicone resin. Examples of materials for inorganic particles include silica, alumina, calcium carbonate, barium sulfate, titanium oxide (titania), and carbon. These materials may be used alone or in combination of two or more. When a non-black material is used, the particles can be made black by coloring them black with an organic or inorganic colorant, such as carbon black, aniline black, or carbon nanotubes. Such colored materials include composite silica, conductive silica, black silica, black acrylic, and the like. Examples of composite silica include nano-level composites of carbon black and silica, conductive silica include silica particles coated with conductive particles such as carbon black, black silica includes natural silica ore containing graphite, and black acrylic includes acrylic copolymers colored with carbon black. In order to obtain better properties, it is preferable to use inorganic particles as the black microparticles. By using inorganic particles as the black microparticles, it is possible to obtain a black light-shielding member with lower gloss and higher blackness. Carbon is preferable as the inorganic particle material used as the black microparticles. Among carbons, it is particularly preferable to use porous carbon particles. By using porous carbon, the following effects can be obtained compared to the use of non-porous black microparticles. That is, light is attenuated by repeated reflection and absorption on the surface and inside of the microparticles, and more low-refractive-index nanoparticles (described later) can be retained on the surface and inside of the black microparticles, thereby further reducing gloss. There are no particular limitations on the shape of the black fine particles, but in consideration of the flow characteristics and coating properties of the coating liquid, and the sliding characteristics of the resulting light-shielding layer, it is preferable to use spherical black fine particles.

[0024] 3) Low refractive index nanoparticles The light-shielding member of the present invention is characterized by containing low-refractive-index nanoparticles. FIG. 2(A) shows the attenuation behavior of incident light in the black light-shielding member of the present invention, and FIG. 2(B) shows the attenuation behavior of incident light in a light-shielding member that does not contain low-refractive-index nanoparticles in the light-shielding layer. As shown in Figure 2(A), in the black light-shielding member of the present invention, a fine uneven shape is formed on the surface of the light-shielding layer by black fine particles. Here, low-refractive-index nanoparticles are dispersed together with the black fine particles in the resin component (binder resin) of the light-shielding layer, and the air-side surface of the black fine particles has a structure in which they are covered with the resin component in which the low-refractive-index nanoparticles are dispersed. Part of the incident light 5 that reaches the surface of the black fine particles through the resin component in which low-refractive-index nanoparticles are dispersed is transmitted and absorbed by the black fine particles, while part of it becomes reflected light. Here, because the black fine particles are covered with the resin component in which low-refractive-index nanoparticles are dispersed, reflection on the surface of the resin component is suppressed. Therefore, compared to the light-shielding member in which the black fine particles are covered with a resin component that does not contain low-refractive-index nanoparticles as shown in Figure 2(B), more light is transmitted through the resin component and more light is absorbed by the black fine particles, which is thought to effectively reduce reflected light. Furthermore, part of the incident light 6 that reaches the surface of the light-shielding layer, which is the interface between the air layer and the resin component that is not coated with black fine particles, is transmitted and part is reflected. Here, in the black light-shielding member of the present invention, low-refractive-index nanoparticles are dispersed in the resin component, so compared to the light-shielding member having a resin component that does not contain low-refractive-index nanoparticles shown in Figure 2(B), the amount of light reflected at the interface between the air layer and the resin component of the light-shielding layer is reduced and the amount of light transmitted through the resin component of the light-shielding layer is increased. The light that has passed through the resin component of the light-shielding layer is reflected at the surface of the substrate, which is the interface between the substrate and the light-shielding layer, and is absorbed by the black fine particles in the light-shielding layer. It is believed that this is why the black light-shielding member of the present invention can achieve low gloss and high blackness. Here, low-refractive-index nanoparticles refer to nanoparticles with a refractive index of 1.5 or less. The average particle size of the low-refractive-index nanoparticles is preferably 1 nm to 200 nm, more preferably 5 nm to 150 nm, even more preferably 10 nm to 100 nm, and most preferably 20 nm to 80 nm. By setting the refractive index and average particle size of the low refractive index nanoparticles within the above ranges, the refractive index of the light-shielding layer can be more effectively reduced, thereby further improving the black color. Conventionally, carbon nanoparticles (n d It is believed that a light-shielding layer containing a fluorine-containing compound (e.g., about 2%) has a high refractive index, which increases the difference in refractive index between the light-shielding layer and the air layer, thereby increasing the amount of diffusely reflected light from the surface of the light-shielding layer. It is also believed that the diffusely reflected light is scattered by the uneven surface of the light-shielding layer, resulting in a whitish appearance and making it difficult to achieve the black color targeted in the present invention.

[0025] The material of the low refractive index nanoparticles may be an inorganic material or an organic material, or may be a mixed material or composite material of an organic material and an inorganic material, as long as it satisfies the above conditions. Examples of inorganic materials include thiolite (Na5Al3F 14 , n d =1.33), cryolite (Na3AlF6, n d =1.35), sodium fluoride (NaF, n d =1.34), lithium fluoride (LiF, n d =1.36), aluminum fluoride (AlF3, n d =1.36), magnesium fluoride (MgF2, n d =1.38), calcium fluoride (CaF2, n d =1.43), barium fluoride (BaF2, n d =1.48), silicon dioxide (SiO2, n d =1.47), calcium carbonate (CaCO3, n d =1.50) and other carbonates. As the organic material, for example, acrylic resin (n d =1.49~1.50), styrene resin, silicone resin (n d =1.43), fluororesin (n d Examples include nanoparticles (submicron particles) such as nanoparticles (approximately 1.35 μm). Furthermore, organic-inorganic hybrid materials (organic-inorganic nanocomposite materials) in which metal oxides and organic molecules are combined can also be used.

[0026] From the viewpoint of chemical stability, it is preferable to use magnesium fluoride, calcium fluoride, lithium fluoride, calcium carbonate, silicon oxide (silica), and the like, among the above-mentioned materials for the low refractive index nanoparticles. Furthermore, hollow nanoparticles, nanoclay particles, etc. can also be used as the low refractive index nanoparticles. In particular, the use of hollow nanoparticles further reduces the refractive index of the light-shielding layer, reducing diffuse reflection and thereby significantly improving blackness. Among these, hollow silica nanoparticles are more preferably used. Alternatively, multiple low-refractive-index nanoparticles with different components can be used. This configuration can further improve the blackness. For example, it has been confirmed that the combined use of magnesium fluoride nanoparticles and silica nanoparticles reduces the L value and improves the blackness compared to when each component is added alone. The reason for this phenomenon is not entirely clear. One possible reason is that when multiple low-refractive-index nanoparticles with different components are used, aggregation of the low-refractive-index nanoparticles is suppressed compared to when they are used alone, resulting in the formation of a light-shielding layer with a low refractive index in which the low-refractive-index nanoparticles are more uniformly dispersed. Another possible reason is that when multiple low-refractive-index nanoparticles with different components are used, one of them easily adheres to the surface of the black particles, primarily reducing the diffuse reflection on the surface of the black particles, while the other easily disperses uniformly in the resin component, reducing the diffuse reflection on the surface of the light-shielding layer, which is the interface between the air layer and the light-shielding layer. This synergistic effect may result in a better blackness.

[0027] The total content of black microparticles 32 and low refractive index nanoparticles 33 in the light-shielding layer 3 of the black light-shielding member 1 of the present invention is not particularly limited as long as the desired characteristics are obtained, but it is preferably 50% to 95% by volume, and more preferably 60% to 90% by volume, of the entire light-shielding layer being 100% by volume. The mixing ratio of the black microparticles 32 and the low-refractive-index nanoparticles 33 is not particularly limited as long as the desired properties are obtained. However, the low-refractive-index nanoparticles 33 are preferably present in an amount of 1 to 50% by volume, and more preferably 2 to 25% by volume, of the total amount of the black microparticles 32 and the low-refractive-index nanoparticles 33. By adjusting the content of the black microparticles and the low-refractive-index nanoparticles in the light-shielding layer within the above range, even better low gloss and blackness can be obtained. Furthermore, within the above range, sufficient adhesion is achieved at the interface between the substrate 2 and the light-shielding layer 3 and at the interface between the particles and the resin component, resulting in excellent processability without peeling of the light-shielding layer during processing. The volume content (volume occupancy) of the low refractive index nanoparticles in the light-shielding layer can also be calculated from a cross-sectional photograph of the light-shielding layer by image analysis or the like, and converted into an area occupancy.

[0028] In the present invention, as constituent components of the light-shielding layer, a leveling agent, a thickener, a pH adjuster, a lubricant, a dispersant, an antifoaming agent, etc. may be further added, if necessary. As the lubricant, in addition to polytetrafluoroethylene (PTFE) particles, which are solid lubricants, polyethylene wax, silicone particles, etc. can be used.

[0029] The above components are added to an organic solvent or water and mixed with stirring to prepare a uniform coating solution. Examples of the organic solvent that can be used include methyl ethyl ketone, toluene, propylene glycol monomethyl ether acetate, ethyl acetate, butyl acetate, methanol, ethanol, isopropyl alcohol, and butanol. The resulting coating solution is applied directly to the surface of the substrate or onto a pre-formed anchor layer, and then dried to form a light-shielding layer. The coating method is not particularly limited, but a roll coater method, a doctor blade method, or the like can be used. The thickness of the light-shielding layer in the present invention is preferably 1 μm to 100 μm, more preferably 2 μm to 50 μm, and even more preferably 3 μm to 25 μm. By setting the thickness of the light-shielding layer within the above range, it is possible to obtain the desired blackness and anti-reflection effect. The thickness of the light-shielding layer refers to the height from the surface of the substrate to the matrix portion of the light-shielding layer that is not protruded by the black fine particles. The thickness of the light-shielding layer can be measured in accordance with JIS K7130.

[0030] The characteristics of the black light-shielding member of the present invention will be described below. (1) Glossiness The glossiness of the surface of the black light-shielding member of the present invention on which the light-shielding layer is formed for light incident at an incident angle of 60° is preferably 1% or less, more preferably 0.8% or less, even more preferably 0.6% or less, and most preferably 0.4% or less. By adjusting the glossiness of the black light-shielding member of the present invention for light incident at an incident angle of 60° within the above range, flare and ghost phenomena due to diffuse reflection of light can be more effectively prevented. The glossiness can be obtained by measuring the specular glossiness at an incident angle of 60° in accordance with JIS Z8741.

[0031] (2) Blackness The L value of the surface on which the light-shielding layer of the black light-shielding member of the present invention is formed is preferably 10 or less, more preferably 8 or less, and even more preferably 7 or less. By adjusting the L value of the black light-shielding member of the present invention to fall within the above range, the blackness is high and the black stands out, resulting in excellent design, and the member can be suitably used as a camera unit for mobile phones such as smartphones. The L value is calculated based on JIS Z8781-4. * a * b * L, which represents lightness in the color space * It's about value.

[0032] (3) Adhesive strength The adhesive strength of the surface of the black light-shielding member of the present invention on which the light-shielding layer is formed is preferably 1 N / 25 mm or more, more preferably 2 N / 25 mm or more, even more preferably 4 N / 25 mm or more, and most preferably 6 N / 25 mm or more. By adjusting the adhesive strength of the black light-shielding member of the present invention within the above range, peeling of the light-shielding layer coating film during processing can be prevented, thereby improving processability. The adhesiveness can be determined by measuring the resistance when 31B tape (manufactured by Nitto Denko Corporation) attached to the light-shielding layer is peeled off in a 180° direction in accordance with JIS Z 0237. The 31B tape can be attached to the light-shielding layer using a 2 kg roller. [Example]

[0033] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the examples, "%" and "parts" indicate % by mass and parts by mass unless otherwise specified.

[0034] <Configuration of black light-shielding member> (1) Base material (1-1) Polyimide film: Kapton 50MBC (thickness 12 μm), manufactured by Toray DuPont (2) Light shielding layer (a) Fine particles (a1) Acrylic filler: average particle size: 3 μm, refractive index: 1.49 (a2) Porous carbon particles: average particle size: 3 μm, refractive index: about 1.55 (a3) Carbon nanoparticles: average particle size: 128 nm, refractive index: 1.82 (a4) Carbon nanoparticles: average particle size: 50 nm, refractive index: 1.80 (a5) Acrylic copolymer fine particles (pigmented type): average particle size: 3 μm, refractive index: approximately 1.50 (b) Low refractive index nanoparticles (b1) Magnesium fluoride: average particle size: 50 nm, refractive index: approximately 1.38 (b2) Hollow silica: average particle size: 60 nm, refractive index: about 1.30 (b3) Silica: Average particle size: 45 nm Refractive index: approximately 1.44 (c) Resin (c1) Acrylic resin: Acrydic A801, manufactured by DIC Corporation (c2) Acrylic resin: Parachron Precoat 200, manufactured by Negami Chemical Industries, Ltd. (c3) Acrylic resin: Parachron W197, manufactured by Negami Chemical Industries, Ltd. (d) Hardener (d1) Polyisocyanate: Takenate D110N, manufactured by Mitsui Chemicals, Inc.

[0035] (Examples 1 to 13, Comparative Examples 1 to 3, Reference Examples 1 and 2) Each component of the light-shielding layer was placed in a solvent and stirred to obtain a coating solution with the blending ratio (solid content by mass) shown in Tables 1 and 2. Methyl ethyl ketone and toluene were used as the solvent. A light-shielding layer was formed by applying a coating solution having the composition shown in Tables 1 and 2 to one side of a polyimide film substrate and then drying it at 120°C for 5 minutes. No anchor layer was provided on the polyimide film, and the coating solution was applied directly to the surface of the substrate. The average film thickness, glossiness at an incident light angle of 60°, L value and adhesive strength of the obtained light-shielding coating film were evaluated by the above-mentioned methods, and the results are shown in Tables 1 and 2.

[0036] Reference Example 1 in Table 1 shows the results of evaluating the characteristics of a sample made with the composition of a conventional light-shielding member. As shown in FIG. 3(A), the light-shielding member 10 of Reference Example 1 has a configuration in which a substrate 20 is coated with a light-shielding layer 30 containing a resin component 331, a matting agent 332, and a black pigment 333. In Reference Example 1, the matting agent 332 is a colorless and transparent acrylic resin particle, and the black pigment 333 is carbon nanoparticles. In such a conventional light-shielding member, it is believed that the fine irregularities on the surface of the light-shielding layer 30 formed by the matting agent 332 scatter light, and the black pigment 333 dispersed in the resin component 331 absorbs light, thereby reducing reflected light and achieving low gloss. However, in Reference Example 1, as shown in Table 1, although the adhesive strength was good at 10.7 N / 25 mm, the gloss at 60° was 2.7% and the L value was high at 23.0, confirming that the low gloss and blackness at the levels targeted by the present invention were not achieved. This is thought to be because the light-shielding layer of Reference Example 1 has a high refractive index due to the dispersed carbon nanoparticles, and the difference with the refractive index of the air layer increases the diffusely reflected light on the surface of the light-shielding layer 30, and the diffusely reflected light is scattered by the uneven surface shape, resulting in a whitish appearance.

[0037] [Table 1]

[0038] Reference Example 2 shows the results of evaluating the characteristics of a sample prepared by adding black porous carbon particles instead of the acrylic resin particles (colorless and transparent) of the matting agent 332 in order to reduce the L value, i.e., improve the black color. As shown in FIG. 3(B), the light-shielding member 100 of Reference Example 2 has a configuration in which a light-shielding layer 300 containing a resin component 3331 and black particles 3332 is coated on a substrate 200. The light-shielding member of Reference Example 2 achieved a low gloss of 0.1% at 60°, and an L value of 8.7, significantly reduced compared to Reference Example 1, demonstrating the achievement of black color. However, the adhesive strength was low at 0.1 N / 25 mm, which is expected to cause problems during processing. In Reference Example 2, as shown in Figure 3(B), in order to reduce the L value to the desired value, the amount of black microparticles 3332 added was increased, which reduced the proportion of resin components in the light-shielding layer 300, and this is thought to be why sufficient adhesion cannot be achieved between the substrate 200 and the light-shielding layer 300, and between the resin components 3331 and the black microparticles 3332.

[0039] In Comparative Example 1, in which half of the black microparticles in Reference Example 2 were replaced with carbon nanoparticles with an average particle size of 50 nm, the gloss at 60° was maintained at a low level of 0.1%, while the adhesive strength increased to 4.8 N / 25 mm. This is believed to be because replacing part of the porous carbon with carbon nanoparticles increased the volume fraction of the resin component in the light-shielding layer, enabling sufficient adhesion between the substrate and the particles. However, in Comparative Example 1, the L value was 18.1, significantly higher than in Reference Example 2, and it was found that the target level of blackness could not be achieved. The reason for this is believed to be that in a light-shielding layer in which carbon nanoparticles with an average particle size of 50 nm and a refractive index of approximately 1.80 were dispersed, the refractive index increased, increasing the refractive index difference with the air layer, resulting in increased diffuse reflection of light from the light-shielding layer surface. The diffuse reflection of light was scattered by the uneven surface of the light-shielding layer, resulting in a whitish appearance.

[0040] On the other hand, in Comparative Example 2, which added transparent acrylic resin particles and low-refractive-index magnesium fluoride nanoparticles, the gloss at 60° was 1.2%, and the L value was 24.4, indicating that the target low gloss and black color could not be achieved. Furthermore, the adhesive strength was 0.2 N / 25 mm, confirming that the adhesiveness was insufficient.

[0041] In contrast, in the examples of the present invention in which low-refractive-index nanoparticles, such as magnesium fluoride nanoparticles (refractive index: 1.38) (Example 1), hollow silica nanoparticles (refractive index: 1.30) (Example 2), and silica nanoparticles (refractive index: 1.44) (Example 3), were added along with black microparticles, all exhibited low gloss at 60°, with an L value of 0.1%, and excellent blackness, with an L value of 8 or less. This is believed to be because the dispersion of low-refractive-index nanoparticles in the light-shielding layer reduced the refractive index of the light-shielding layer, thereby reducing the refractive index difference with the air layer, thereby reducing the diffusely reflected light on the surface of the light-shielding layer. Furthermore, the diffusely reflected light was absorbed and reflected by the black microparticles, resulting in significant attenuation of light. Furthermore, in all examples of the present invention containing black microparticles and low-refractive-index nanoparticles, the adhesive strength was 3 N / 25 mm or more, confirming good adhesion. Among Examples 1 to 3, Example 2, which used hollow silica with a refractive index of 1.30, showed a decrease in L value to 6.3, excellent blackness, and a high adhesive strength of 5.9 N / 25 mm. This is thought to be because the low refractive index of the hollow silica nanoparticles further reduced the refractive index of the light-shielding layer, reducing the difference with the refractive index of the air layer and further reducing diffuse reflection of light on the surface of the light-shielding layer. In this example, porous carbon is used as the black microparticles, and it is believed that light is reflected and absorbed between the porous carbon microparticles, and that the light is also reflected and absorbed repeatedly within the porous carbon microparticles (within the pores), resulting in significant attenuation of light and further improving the blackness.

[0042] Furthermore, it was confirmed that Example 4 (magnesium fluoride nanoparticles and hollow silica nanoparticles), Example 5 (magnesium fluoride nanoparticles and silica nanoparticles), and Example 6 (hollow silica nanoparticles and silica nanoparticles), in which two types of low refractive index nanoparticles were added, also had low gloss and excellent black color and adhesiveness. In particular, Example 4, in which magnesium fluoride nanoparticles and hollow silica nanoparticles were added, had an L value of 5.4, which was lower than the L values ​​of Example 1, in which magnesium fluoride nanoparticles were used alone, and Example 2, in which hollow silica nanoparticles were used alone, confirming the effect of using multiple low-refractive-index nanoparticles with different refractive indices in combination. It was also found that Example 4, in which magnesium fluoride nanoparticles and hollow silica nanoparticles were added, had improved adhesiveness compared to Example 1, in which magnesium fluoride nanoparticles were used alone, and Example 2, in which hollow silica nanoparticles were used alone. Furthermore, it was found that Example 5, in which magnesium fluoride nanoparticles and silica nanoparticles were added, also had an L value lower than both Example 1, in which magnesium fluoride nanoparticles were used alone, and Example 3, in which silica nanoparticles were used alone, and achieved a black color equivalent to that of Example 2, in which hollow silica nanoparticles were added. Furthermore, Example 5 had a higher adhesive strength than both Example 1 and Example 3, and also improved adhesiveness compared to Example 2. This confirmed that by using magnesium fluoride nanoparticles and silica nanoparticles in combination, low gloss, excellent black color, and adhesiveness can be achieved without using expensive hollow silica nanoparticles. The reason why the L value is reduced when multiple low-refractive-index nanoparticles with different components and refractive indices are used is unclear, but it is thought to be as follows. One reason is that using multiple low-refractive-index nanoparticles of different types prevents aggregation of the low-refractive-index nanoparticles compared to using a single type, resulting in a low-refractive-index light-blocking layer in which the low-refractive-index nanoparticles are more uniformly dispersed. Another reason is that when multiple low-refractive-index nanoparticles with different components are used, one type tends to adhere to the surface of the black particles, while the other type tends to disperse uniformly in the resin component. For example, in Example 5, which combined magnesium fluoride nanoparticles and silica nanoparticles, the magnesium fluoride nanoparticles adhered to the surface of the black particles, reducing the diffuse reflection on the surface of the black particles, while the silica nanoparticles dispersed in the resin component, reducing the diffuse reflection on the surface of the binder resin of the light-blocking layer, which is the interface between the air layer and the light-blocking layer. The synergistic effect of these two nanoparticles is thought to result in even better blackness.

[0043] In Examples 7, 5, and 8 in Table 2, samples were prepared by varying the amount of low-refractive-index nanoparticles added while keeping the amounts of black microparticles and resin components constant. Here, magnesium fluoride nanoparticles and silica nanoparticles were used as the low-refractive-index nanoparticles, with a mass ratio of 1:1. In all of Examples 7, 5, and 8, low gloss was achieved with a 60° gloss of 0.1. The L value was 6.3 in Example 5, in which 50 parts by mass of magnesium fluoride nanoparticles and 50 parts by mass of silica nanoparticles were added. In contrast, the L values ​​in Example 7, in which 25 parts by mass of magnesium fluoride nanoparticles and 100 parts by mass of silica nanoparticles were added, were 8.5 and 7.8, respectively, which were found to be higher than in Example 5. In Example 7, the amount of low-refractive-index nanoparticles was reduced, which is thought to have increased the refractive index of the light-shielding layer, increased the amount of diffusely reflected light, and resulted in a high L value. On the other hand, in Example 8, the amount of low-refractive-index nanoparticles was increased, which is thought to have reduced the proportion of black fine particles in the light-shielding layer, suppressing the reflection and absorption of diffusely reflected light and resulting in a high L value. Furthermore, the adhesive strength increased in the order of Examples 7, 5, and 8. It was found that, when the amount of black fine particles in the light-shielding layer was kept constant, the adhesive strength of the light-shielding layer improved by increasing the amount of low-refractive-index nanoparticles. This is thought to be because the binder resin became tougher due to the incorporation of low-refractive-index nanoparticles. From the above results, it was found that adjusting the content of low refractive index nanoparticles in the light-shielding layer is effective in obtaining the desired black color and adhesiveness.

[0044] Examples 9, 5, and 10 in Table 2 show the results of evaluating gloss, L value, and adhesion when the ratio of magnesium fluoride nanoparticles to silica nanoparticles is varied while the total amount of magnesium fluoride nanoparticles and silica nanoparticles is kept constant. For comparison, the results of Examples 1 and 3, in which magnesium fluoride nanoparticles and silica nanoparticles were added alone, are also shown. Compared to Examples 1 and 3, in which magnesium fluoride nanoparticles and silica nanoparticles were added alone, Examples 9, 5, and 10, in which magnesium fluoride nanoparticles and silica nanoparticles were added, showed a decrease in L value, indicating improved adhesion. No significant differences were observed in the L value between Example 9, in which the ratio of magnesium fluoride nanoparticles was 25% by mass, Example 5, in which it was 50% by mass, and Example 10, in which it was 75% by mass, assuming the total amount of magnesium fluoride nanoparticles and silica nanoparticles to be 100. When magnesium fluoride nanoparticles are used alone, there is a possibility that the refractive index may be uneven in the light-shielding layer due to aggregation of the magnesium fluoride nanoparticles. However, by adding silica nanoparticles, the aggregation of the magnesium fluoride particles is broken down, forming a low-refractive-index light-shielding layer in which low-refractive-index nanoparticles are uniformly dispersed throughout the light-shielding layer. This is thought to further reduce diffuse reflection and further improve blackness. Furthermore, in Examples 9, 5, and 10, which contained magnesium fluoride nanoparticles and silica nanoparticles, it is thought that the magnesium fluoride nanoparticles adhered to the surface of the black particles and reduced the diffuse reflection from the surface of the black particles, while the silica nanoparticles dispersed in the resin component and reduced the diffuse reflection from the surface of the binder resin of the light-shielding layer, which is the interface between the air layer and the light-shielding layer, and that the synergistic effect of these two factors may have resulted in even better blackness.

[0045] Examples 11, 5, and 12 in Table 2 show the results of evaluating the gloss, L value, and adhesiveness when the ratio of porous carbon, magnesium fluoride nanoparticles, and silica nanoparticles was kept constant and the total content of these particles relative to the light-shielding layer was varied. In all examples, a low gloss was obtained with a 60° gloss ratio of 0.1%. Furthermore, in Example 11, where the particle content relative to the light-shielding layer was 69% by volume, the L value was 8.7 and the adhesiveness was 11.8 N / 25 mm, confirming good black color and excellent adhesiveness. In Example 5, where the particle content was 82% by volume, the L value decreased to 6.3 and the adhesiveness decreased to 6.7 N / 25 mm. Furthermore, in Example 12, where the particle content was 85% by volume, the L value was 6.4, equivalent to Example 5, but the adhesiveness decreased to 2.1 N / 25 mm. From the above results, it was found that adjusting the total amount of black fine particles and low refractive index nanoparticles in the light-shielding layer is effective in obtaining the desired blackness and adhesiveness.

[0046] Table 2 shows the results of a similar evaluation of Comparative Example 3, in which black-colored acrylic resin particles were used instead of porous carbon as the black particles and dispersed in the resin layer together with carbon nanoparticles. In Comparative Example 3, the gloss at 60° was 0.2% and the adhesion was 9.8 N / 25 mm, indicating sufficient low gloss and adhesive strength. However, the L value was 13.6, indicating that the target blackness was not achieved. This is thought to be due to the high refractive index of the light-shielding layer in which carbon nanoparticles are dispersed, resulting in a lot of diffuse reflection on the surface of the light-shielding layer. The results of Example 13, which used black-colored acrylic resin microparticles and low-refractive-index nanoparticles, magnesium fluoride nanoparticles and silica nanoparticles, are also shown in Table 2. In Example 13, the 60° gloss was 0.1%, the L value was 9.7, and the adhesion was 10.1 N / 25 mm. This confirmed that the effects of the present invention, such as low gloss, excellent blackness, and adhesion, could be obtained even when black-colored acrylic resin microparticles were used as the black microparticles.

[0047] [Table 2] [Explanation of symbols]

[0048] 1, 10, 100 Light blocking material 2, 20, 200 base material 3, 30, 300 light shielding layer 31, 331, 3331 Resin component 32, 3332 Black fine particles 33 Low refractive index nanoparticles 332 Matting agent 333 Black pigment

Claims

1. A black light-shielding member comprising a substrate and a light-shielding layer formed on at least one surface of the substrate directly or via an anchor layer, the light-shielding layer contains black fine particles, low-refractive-index nanoparticles, and a resin component; the black fine particles contain porous carbon, The black light-shielding member is characterized in that the low refractive index nanoparticles contain magnesium fluoride particles and silicon oxide particles.

2. The black light blocking member according to claim 1 , wherein the low refractive index nanoparticles include hollow nanoparticles.

3. The black light-shielding member according to claim 2 , wherein the hollow nanoparticles include hollow silica particles.

4. A black light-shielding member according to any one of claims 1 to 3, characterized in that the total content of the black microparticles and low refractive index nanoparticles in the light-shielding layer is 50% to 95% of the volume of the entire light-shielding layer.

5. The black light-shielding member according to any one of claims 1 to 4, characterized in that the black microparticles have an average particle size of 0.1 μm to 50 μm, the low-refractive-index nanoparticles have an average particle size of 1 nm to 200 nm, and the low-refractive-index nanoparticles occupy 1 volume % to 50 volume % of the total amount of the black microparticles and the low-refractive-index nanoparticles.

6. A black light-shielding member as described in any one of claims 1 to 5, characterized in that the glossiness of the surface on which the light-shielding layer of the black light-shielding member is formed for incident light at an incident angle of 60° is 1% or less, and the L value is 10 or less.

7. 7. The black light-shielding member according to claim 1, wherein the light-shielding layer has an average thickness of 1 μm to 100 μm.

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